题材：科学普及

关键词：地质年代、恐龙、陨石坑、证据

河北地质大学教授 丁毅

开始写作：201124 ，最后更新：210119

1. Geological Times (地质年代) and dinosaur disappearance

4600Ma/24 = 192ma=1.9亿年

The earth starts 46, 46-25（Archean）, 25-5.7 (Proterozoic), 5.7(21)-4 (Paleozoic: Cam, O, S, invertebrate), 4-2.5(Paleozoic: D, C, P, vertebra), 2.5-0.65 (Mesozoic: T, J (2.08(22.52)-1.35), K (1.35-0.65(22.37)), Dinosaur, Ammonite), 0.65(23.37)-now (Cenozoic, mammal, human: 0.0248 (23.5672))

(4600-570)/192 = 21, Trilobites

(4600-140)/192 = 23.23(23:14) Dinosaur

(4600-65)/192 = 23.62 (23:37) Dinosaur disappearance

K/T boundary,,,,,

(4600-2)/192 = 23.95 (23:57) man from late Paleolithic age (晚更新世时期)

570Ma, England

2. Meteor impacts affecting lifes on the earth

3. Alvarez父子和高Ir元素含量层：

170km in diameter. 341 scientists and workers are working on it.

墨西哥境内的尤卡坦半岛Chicxulub陨石坑，又称为“恐龙陨石坑”，直径有198km, 是6500万年前一颗直径为10-13km的小行星撞击地球而成，导致恐龙灭绝, 形成K/T分界线 (Lowery, et al. 2018；Renne et al.2018）和高Ir元素含量层（Alvarez et al., 1980），也被认为是当时全球变冷的主要原因（Brugger et al.2017) 。该陨石坑为重力负异常（Gulick, et al.2013）、存在地震反射波（Connors et al. 1996）和地震折射波异常（Gulick et al.2013），中心峰附近的岩浆热液活动有可能是陨石冲击造成的（Kring, et al.2017）。世界上所发现的大型陨石坑为数不多，其它大型陨石坑还有加拿大的Sudbury (Lenauer and Riller,2012) 和南非的Vredefort (Grieve et al.,2008）。
4. Meteor impact craters on planets

1994 on Jupiter

moon

嫦娥五号，201205

mars

How about the earth?

5. Evidence

地球上风化严重，可能的陨石坑地貌形态消失，但是我们可以观察月球和火星上的，，，

Owing to strong weathering on the earth, we could get some peeks on other planets such as Mars and moon to understand what topography of a meteor pit looks like.

A gaint meteor impact on the moon.

The Mare Moscoviense Basin is a circular area on the far side of the Moon with a diameter of 445 kilometers (Figure 1). Mare Moscoviense is an area of smooth lava within the basin with an outline of three overlapping circles. The largest circle is approximately 160 kilometers in diameter, the second circle is 120 kilometers in diameter, and the smallest circle is 90 kilometers in diameter (Figure 2). Within the large circle of smooth lava, there are several impacts of about 15 kilometers in diameter, some of which overlap.

Landforms, Simple and Complex, Coesite, PDFs, Meteor stream or blocks, Tektites (moldavite) strew or splash field

Shatter cones，为高温高压冲击变质所产生的一种特殊的岩石形体，从小于1厘米到15厘米或更大，呈锥体形状，表面有很多沟槽，顶端为钝尖，指向陨石与岩石碎块摩擦冲击的方向（图2d,2h）。在复杂陨石坑，且坑底原岩是石灰岩、白云岩、石英岩、片麻岩和页岩，可以见到震裂锥，震裂锥被认为是陨石坑的可靠证据(Chen, et al.2016; Dietz, 1960, 1968; Hargraves,1961; Hargraves, et al.1990; Gash,1971; Gibson,1998; French,2005; Osinski,2007; Osinski and Ferrière,2016)。

PDF

目前每年有大约1万到8万颗陨石袭击地球（Monthly Notices of the Royal Astronomical Society）。地球大气圈的保护、板块运动、岩浆溢流、沉积物的掩埋、风化剥蚀、海洋淹没等使得地质科学家在地球陆地上发现陨石坑要比在月球上发现陨石坑困难得多 (Grieve, 1987, 2001)。1976年中国吉林市北郊发现的3000多块陨石中，最大的一块陨石重约1.77吨，砸出了一个2米长6.5米深的陨石坑。

大多数陨石是石质陨石（stony meteorites），分为球粒陨石（chondrites）和无球粒陨石（achondrites），只有约6%的陨石是铁陨石（iron meteorites）或岩石和金属的混合物，即石铁陨石 (stony-iron meteorites)(Krot et al.2007)。陨石冲过地球大气圈的摩擦后，虽然燃烧耗尽，但是仍然会有陨石落到陨石坑附近，尤其在简单陨石坑（澳大利亚的Wolfe Creek陨石坑和美国的Barringer陨石坑）附近能找到陨石的残留物，而在大型陨石坑内却很少，这可能是陨石与地面冲撞时，易于爆炸后蒸发有关。在南极的冰盖上无土背景和陨石颜色与冰盖的白色强烈对比，较易发现陨石（Yoshida,2010）。1976年3月8日，我国吉林省吉林市近郊发生了大规模的陨石雨，陨落区直径70多km，面积在400～500平方km之间，共收集到陨石100多块，总重2616千克，其中“吉林1号”陨石重1770千克。

6. 全球：190 as in the year of 2020（截至到2020年1月1日）Nature of published diagnostic evidence: coesite and stishovite, directly associated meteorite, Morphology, breccias, impact melts.

南非的Vredefort陨石坑具有中心峰（图2e，2L），由花岗岩组成的中心峰直径大约70km, 形成约180-300km直径, 是元古代形成的，是人类认知的最老最大的陨石坑 (Erickson et al. 2013）

Clearwater Lakes陨石坑，这是一对孪生陨石坑，形成在2亿9千万年以前，可能是由分裂成两块的小行星同时撞击地球而成。东南的陨石坑直径22km，西北的陨石坑直径32km, 后者具有中心峰的环状地貌，简称“峰圈”（图2k），它们在奥陶纪形成（Schmieder2014)，坑内外岩石多种元素(Os, Ir, Ru, Rh and Pd) 高于地壳平均值, Schmidt（1997），还富含PGE, Ni, Au（Tangle and Hecht，2006), 石英具有PDF（Clutson et al.,2018）。

7. 著名的BARRINGER CRATER, ARIZONA

The famous 'Meteor Crater' of Arizona.  The Barringer Crater is a 1.2 kilometer simple, bowl shaped crater formed about 50,000 years ago by an iron impactor about 30 meters across.

Many fragments of iron-nickle meteorite associated with the impact have been found at this crater.    Chao, E. C. T., Shoemaker, E.M. and Madsen,B.M., First natural occurrence of coesite. Science, v. 132, pp. 220-222.

Chao, E. C. T., Fahey, J.J., Littler, J. and Milton,D.J., Stishovite, SiO2, a very high pressure new mineral from Meteor crater, Arizona. Journal of Geophysical Research, v. 67, pp. 419-421. 1962.

8. 地球在历史上，小行星日纪念1908 Tunguska impact

Asteroid Day （小行星日，每年6月30日）

Asteroid Day marks the anniversary of the 1908 Tunguska impact (see the following photo)，0630.  21443 asteroids pose threats to humanity and any larger than 10 meters could explode on our planet. Asteroid Day events are largely independently organized around the world for people of all ages and are mostly free-of-charge. Asteroid Day is a program run by the Asteroid Foundation, a Luxembourg nonprofit organization.

https://zh-prod-1cc738ca-7d3b-4a72-b792-20bd8d8fa069.storage.googleapis.com/s3fs-public/inline-images/tunguska-event-wide.jpg

1908 Tunguska impact

4179 Asteroid
小行星4179（4179 Toutatis），又称“4179 图塔蒂斯”（或“4179 托搭提斯”），长度为4.46公里，宽2.4公里，外形看起来像是一颗花生。

(some words: meteor crater/pit, meteor stream, meteor shower)

http://craterexplorer.ca/meteorite-glossary/

9. 简单和复杂陨石坑的特点, crater morphology - simple and complex

some milestones:

- The work of Dietz (1959 and 1960) crystallized the concept of complex impact craters, with identification of a group of 7 related structures identifiable by a central uplift that contained shatter cones.

- Chao et al. (1960) found coesite, a high pressure mineral polymorph of quartz, at Meteor Crater, Arizona (Barringer crater).

- Terrestrial (Earth) craters with a 'simple' morphology tend to be 4 km or less in diameter and have a bowl shaped depression with a raised rim.  Craters with a complex morphology, depending on impacted rock type, tend to be a minimum of about 4 kilometers in diameter,

- Craters between 5 and 15 km in diameter characteristically express complex crater morphologies , a central peak and surrounding bowl that rises again to a raised outer crater rim. All of the primary deformation and faulting in craters of this scale occurs within 15 to 60 seconds.  (Kenkmann, 2002). Larger craters have a lower depth to diameter ratio.  Simple Craters (typically less than 1/2 km up to 2.5 to 4 km Bowl shaped depressions with a raised rim.

Dietz R. S. 1946. Geological structures possibly related to lunar craters. Popular Astronomy, Volume 54, pages 465-467；Dietz R. S. 1947. Meteorite impact suggested by the orientation of shatter-cones at the Kentland, Indiana disturbance. Science 105: 42-43.  DOI: 10.1126/science.105.2715.42

Melosh, H. J. and Ivanov, B. A., 1999, Impact Crater Collapse, Annu. Rev. Earth Planet Sci. 27 pp. 385-415

Pike, R. J., 1980, Control of crater morphology by gravity and target type: Mars, Earth, Moon, Proc. Lunar Planet. Sci. Conf. 11th pp. 2159-2189

There are many natural processes other than impacts that can create circular features and depressions on the surface of the Earth. Examples include glaciation, volcanism, sinkholes, atolls, salt domes, intrusions, and hydrothermal explosions (to name just a few). Prehistoric mines and quarries are also sometimes mistaken for impact craters.

http://craterexplorer.ca/meteorite-glossary/

https://www.geographyrealm.com/impact-craters/

Bevan French's book:Traces of Catastrophe,' and Osinski and Pierazzo's (editors) recent volume 'Impact Cratering Processes and Products'

http://www.lpi.usra.edu/publications/books/CB-954/CB-954.pdf

The most sucessful geopark so far on the earth。

10 China

from Professor Wu Siben